1. Field of the Invention
The present invention relates to a data communication apparatus and data communication method used in a digital radio communication system using a CDMA (Code Division Multiple Access) system and so on.
2. Description of the Related Art
Conventionally, in a data communication method, a plurality of received signals provided from a plurality of antennas are synthesized by multiplying each received signal by weights. This processing forms the reception directivity and suppresses unnecessary signals to prevent reception performance from deteriorating.
As a configuration of such antennas, there is an adaptive array antenna apparatus. Since the adaptive array antenna apparatus has a function to cancel an affect of multi-path fading and so on, it can reduce a communication performance deterioration caused by interference and multi-path propagation in radio signal environments of mobile communications. As the number of antennas in the adaptive array antenna, 2 to 10 antennas are usually applied, however 2 to more than 1,000 antennas are sometimes applied.
FIG. 1 is a block diagram illustrating a configuration of a conventional data communication apparatus. In FIG. 1, signals received at plural antennas 1 are subjected to a predetermined radio reception processing, then input to weight controller 2 and multipliers 3 and 4.
Weight controller 2 calculates weights, by which the plurality of signals received at plural antennas 1 are weighted, corresponding to electric field intensities and the phase of received signals and outputs the calculated weights to multipliers 3 and 4. In addition, directions from which radio signals are transmitted, i.e., the radio signal's direction of arrival are estimated by calculating the weights.
Multipliers 3 and 4 multiply the received signals by the weights. Adder 5 adds the multiplication results in multipliers 3 and 4 and outputs the addition result to propagation path distortion compensator 6.
Propagation path distortion compensator 6 estimates a radio signal distortion caused in a propagation path using the addition results, compensates the estimated distortion, and outputs the received signals subjected to the distortion compensation to weight controller 2 and detector 7.
Detector 7 detects the received signals subjected to the distortion compensation and outputs the detected results as received signals to a received signal processing circuit (not shown), while outputs weights to synthesize the received signals provided via plural antennas 1 to weight controller 2 to update a parameter of weight controller 2.
However, in the above conventional data communication apparatus, in the case where a channel quality deteriorates by a rapid change of the radio signal's direction of arrival and so on, other antenna synthesis weights are calculated. At this time, the channel quality deteriorates when a value obtained before the radio signal is switched is used because incoming directions of arrival are different. Hence, weight controller 2 can not use the value obtained before the radio signal is switched as an initial value. Therefore an initial synthesis of received signals after the radio signal is switched should be performed without directivity. Hence desired radio signals are affected by interference signals of the same channel transmitted from different directions, thereby deteriorating the reception performance.